The present invention relates to a coordinate measuring machine for measuring a measurement object, comprising a workpiece support for supporting the measurement object, comprising a measuring head carrying an optical sensor, wherein the measuring head and the workpiece support are movable relative to one another, wherein the optical sensor has a objective and a camera, which is designed to capture an image of the measurement object through the objective, wherein the objective has a light entrance opening and a light exit opening, wherein the objective has a multitude of lens-element groups which are arranged in the objective between the light entrance opening and the light exit opening one behind another along a longitudinal axis of the objective.
The use of optical sensors in conjunction with coordinate measuring machines makes it possible in many cases to measure geometrical properties of a measurement object very rapidly. One disadvantage of known coordinate measuring machines comprising optical sensors heretofore has been that the optical sensors are limited to specific measurement tasks and specific workpiece properties. The optical sensors are generally optimized for a specific type of measurement task, for instance with regard to the achievable measurement accuracy or the measurement range. Problems can be posed for example by workpieces which have large height differences parallel to the optical axis of the sensor. In part, different optical and/or tactile sensors are used in order to be able to react flexibly to different measurement requirements, wherein the individual sensors in each case perform only part of the overall measurement task. In general, each individual sensor is optimized towards a specific measurement task. Primarily optical sensors therefore have a respective individual optics which is well suited to a specific purpose of use and is less well suited to other purposes.
By way of example, coordinate measuring machines comprising a white light sensor have been proposed. Such a coordinate measuring machine is disclosed by the document DE 103 40 803 A1, for example.
Most of the confocal white light sensors used are point sensors. These sensors achieve a depth resolution in a range of less than 1 μm to approximately 20 mm. A resolution in such an operating range can typically be represented by approximately 15 bits. Such sensors are used to perform precise measurements along scanning paths on a measurement object. Often, measurement results of these sensors are combined with camera images. The advantages of fast surface information and very accurate depth information can be combined in this way. Embodiments in which a plurality of measurement channels or measurement points are arranged alongside one another are also known. However, the individual measurement points generally have a relatively large lateral distance, with the result that a measurement with a genuine, solid line is not possible.
On the other hand, it has also been proposed to direct a line of white light onto a measurement object. In this case, the different colours of the light within the available spectrum are imaged into different depths. The light reflected by the measurement object is subsequently analysed spectrally and a respective measurement point is assigned the depth value as measurement value for which the reflected spectral light distribution has its maximum value.
As explained in the document DE 103 40 803 A1, such white light sensors are arranged in addition to the other optical sensors on the carrier structure of the coordinate measuring machine.
The provision of different sensors for different measurement tasks in a coordinate measuring machine makes possible a high flexibility in conjunction with a high measurement accuracy. The high costs for the provision of the numerous sensors with in each case a dedicated optics adapted to the purpose of use of the sensor are disadvantageous. Furthermore, the large number of sensors with in each case a dedicated optics require a relatively large structural space in the coordinate measuring machine, which restricts the measurement volume and causes further costs.
There is a desire to provide an optical coordinate measuring machine which can perform a large range of optical measurement tasks in conjunction with comparatively low costs. Accordingly, it is an object of the present invention to specify a corresponding coordinate measuring machine and a corresponding method.